WATER CONSUMPTION AND OPTIMIZATION OF THE IRRIGATION IN ORCHARDS.

Two experiments were conducted: one in Clermont-Ferrand (central France) with 2 years old walnut trees (Juglans regia L; cv "Lara"), potted in 200 l containers and subjected to normal and drought conditions and other in Reus (Spain) with 5 years old walnut trees (Juglans regia L; cv "Serr"), under field conditions and submitted to unlimited and water stress applications.

The heat balance method is used to estimate the sap flow in trees. Water consumption is calculated in walnut trees under unlimited water supply and water deficit conditions. This technique is very usefulness to estimate the water requirements of the trees and allows to study the water relations in plants, specially in drought conditions.

Three differents water stress indicators (daily variation of stem diameter, predawn leaf water potential and sap flow rate) are tested in order to determine the best indicator for irrigation scheduling. The first results shows that the three methods are interesting for this purpose.